1. Field of the Invention
The present invention relates to measuring methods, measuring systems, inspecting methods, inspection systems, exposure methods and exposure systems, and more particularly to a measuring method and a system in which information related to the degree of flatness of an object used for exposure is measured, an inspecting method and a system in which an object used for exposure is inspected for foreign materials or partial defects, and an exposure method and an exposure system using the measuring method and the inspecting method.
2. Description of the Related Art
In a lithography process for manufacturing semiconductor devices, liquid crystal display devices, and the like, an exposure apparatus that transfers a pattern formed on a mask or a reticle (hereinafter generally referred to as a ‘reticle’) onto a substrate such as a wafer, a glass plate, or the like on which a resist or the like is coated (hereinafter generally referred to as a ‘wafer’) via a projection optical system, as in for example, a sequentially moving type exposure apparatus such as a reduction projection exposure apparatus by the step-and-repeat method (the so-called stepper), or a scanning projection exposure apparatus by the step-and-scan method (the so-called scanning stepper), which is an improvement of the stepper, is mainly used.
In the projection optical system of such types of projection exposure apparatus, because resolution close to the limit is required, in recent years, the numerical aperture (NA) of the projection optical system is largely set so as to improve the resolution, which makes the depth of focus (DOF) fairly shallow. As a consequence, this tightens the requirement accuracy of focus leveling control in which the exposure surface of the wafer is positioned within the depth of focus in the direction of the optical axis of the projection optical system.
In such a situation, even a slight deformation of the reticle cannot be overlooked. For example, when the target position of the wafer in the direction of the optical axis of the projection optical system is arranged at the same position for the entire pattern area, if, in the case the surface (pattern surface) of the pattern area of the reticle is uniformly bent to the projection optical system side, then the exposure surface will fall outside the depth of focus and defocus will occur partially.
Further, when deformation of the pattern surface occurs in the reticle, the image-forming position of the pattern on the pattern surface in the direction perpendicular to the optical axis of the projection optical system may also change (lateral deviation), and such lateral deviation of the pattern may also be the cause of distortion errors.
From the background described above, requirements are pressing for a more accurate control in the degree of flatness of the reticle. For example, one example is the art of devising holding methods of the reticle in a reticle holder (for example, Kokai (Japanese Unexamined Patent Application Publication) No. 2004-328014)). Further, a standard is rigidly set, which is related to the degree of flatness of the reticle according to the transfer accuracy of the pattern required, and as its qualifying standard, for example, the degree of flatness, which is expressed as the difference between the maximum value and the minimum value of the reticle surface, is to be within 0.5 micron.
This standard, however, is a standard that is related to the degree of flatness of the reticle itself, and during the actual exposure, the degree of flatness further decreases due to the following reasons:
(a) flexure due to the weight of the reticle itself,
(b) reticle deformation that occurs when the reticle is forcibly held by suction by the reticle holder (platen) due to different degree of flatness of the contact surface of both the reticle and the reticle holder.
Because the deformation of the reticle held by the reticle holder is different in each reticle, or further different in each reticle holder in the exposure apparatus (substantially synonymous with each equipment), in order to obtain information related to the degree of flatness of the reticle on exposure, there is no way but to measure the reticle used in exposure in a state where the reticle is actually held by suction by the reticle holder of the exposure apparatus. In this case, however, because the process of measuring the deformation of the reticle after the reticle is held on the reticle holder will have to be performed during the series of exposure processes, concern of the throughput declining in the exposure process arises.